Some math on the average level 6 gank
At level 6, most champions have about 900-1000 HP if they haven't purchased any health besides a doran item. Most champions will have around 25% damage reduction in both resistances, give or take. You get either 12 AD or 20 AP from runes
Ignite: 205 true damage Chilling Smite: 68 true damage Electrocute: 74 (+0.25 AP, 0.4 bonus AD) adaptive damage
post mitigation this comes out to 335 damage when you include AP or AD from a starting item and runes. This is over 1/3 of many champs level 6 HP that is completely independent from the champion's kit
If the enemy jungler has red buff and lands a single autoattack, that total goes up to 377. If your lane opponent got a Hextech Revolver (a very common rush item for AP assassins), that total is now 439.
The highest HP champs at level 6 get around 1100. They often have a Dshield, so 1220. This is still 36% of their HP after mitigation Squishies are more likely to have about 900 HP, or 980 after Dring/Dblade This is 45% of their HP after mitigation
We have a situation where a champion can take anywhere from 1/3 to nearly 1/2 of their HP from damage sources that have nothing to do with the opposing champion and are all essentially targetted.
But there isn't too much damage flying around. No.
PS: Someone will say "You're 2v1, you should lose". Well no shit. There's a difference between "you should lose" and "almost half their damage doesn't actually come from their kits". I'm not advocating that a champion should be able to 2v1 without an outplay. I'm saying that you should be playing against the opponent's champion, not their runes and summoner spells.